1. Field of the Invention
The present invention relates to a method for manufacturing a liquid crystal display and, more particularly, to a method for manufacturing a liquid crystal display whose liquid crystal is sealed between two substrates using a dispense-injection process.
2. Description of the Related Art
Among liquid crystal displays, active matrix type color liquid crystal displays utilizing thin film transistors (TFTs) as switching elements are attracting attention as the mainstream of flat panel displays, and there is a need for a method for manufacturing them with high quality on a mass production basis.
General processes for manufacturing liquid crystal displays are an array process at which wiring patterns and switching elements such as thin film transistors are formed on glass substrates (in the case of the active matrix type), a cell process at which an alignment process is performed; spacers are provided; and liquid crystals are encapsulated between glass substrates opposite to each other and a module process at which driver ICs and a back-light are mounted.
The step of providing spacers at the cell process employs either a method in which a multiplicity of spherical particles in the form of beads are dispersed on the surface of the substrates or a method in which columnar spacers are formed on either or both of the glass substrates opposite to each other instead of the spherical particles. The spacers formed using such methods are used for maintaining a constant cell gap (cell thickness) between the glass substrates opposite to each other.
The step of injecting liquid crystals employs a method in which an array substrate having TFTs formed thereon and an opposite substrate having color filters (CFs) and so on formed thereon are combined in a face-to-face relationship using a sealing agent; the sealing agent is thereafter hardened; the liquid crystals and substrates are then put in a vacuum chamber; the atmospheric pressure is restored in the chamber after an injection port provided in the sealing agent is immersed in the liquid crystals to encapsulate the liquid crystals between the substrates (vacuum injection method).
Recently, the dispense-injection method is attracting attention in which a prescribed quantity of liquid crystals are dispensed on a surface of an array substrate within a frame of a main seal formed like a frame around the substrate and in which liquid crystals are filled by encapsulated them after the array substrate and an opposite substrate are combined in the vacuum. In comparison with the vacuum injection method used widely in manufacturing liquid crystal displays, the dispense-injection method can possibly reduce costs for manufacturing liquid crystal display panels and improve productivity on a mass production basis because, first, it can significantly reduce the amount of a liquid crystal material to be used and, second, it can decrease the time required for injecting liquid crystals, and a strong demand therefore exists for the use of the dispense-injection method at steps for manufacturing liquid crystal display panels.
According to the dispense-injection method, a predetermined quantity of liquid crystals are dispensed on a substrate using a liquid crystal dispenser. However, a problem can arise in that the quantity of liquid crystals encapsulated between two substrates to be combined can become excessive or insufficient because of the dispensing accuracy of the dispenser and variation of the cell gap. A shortage of the quantity of encapsulated liquid crystals results in so-called foams. Irregularity of display can occur when the quantity of encapsulated liquid crystals is excessive. Any panel having such foams and irregularity of display is regarded as defective.
According to the method of maintaining a cell gap using columnar spacers, support posts made of resin having a height of several microns are formed on substrates, and the height (thickness) of the support posts is likely to vary from substrate to substrate. When the height of the support posts significantly varies from substrate to substrate, a situation can occur in which a quantity of liquid crystals set to be dispensed for a certain substrate is excessive or insufficient for another substrate when the quantity is applied as it is. Even in the case of a multi-shot substrate that is a single glass substrate from which a plurality of liquid crystal display panels are formed, variation of the height of support posts can occur between regions in which display panels are to be formed. For this reason, the optimum quantity of liquid crystals to be dispensed can be different between the regions in which display panels are to be formed in the multi-shot glass substrate.
According to the method for maintaining a cell gap by dispersing beads, although spherical particles having substantially the same size are used, the quantity of dispensed liquid crystals can vary like the above-described case because the quantity of liquid crystals encapsulated between two substrates to be combined varies depending on the number of dispersed beads (dispersing density).
It is an object of the invention to provide a method for manufacturing a liquid crystal display that is a dispense-injection method in which liquid crystals can be dispensed in an optimum quantity on each substrate.
The above-described object is achieved by a method for manufacturing a liquid crystal display in which liquid crystals are injected by dispensing liquid crystals on a substrate and recovering the atmospheric pressure after combining the substrate with an opposite substrate in vacuum with the liquid crystal dispensing surface thereof facing the opposite substrate, characterized in that an optimum quantity of liquid crystals encapsulated between the two substrates to be combined is predicted based on the state of the substrate on which the liquid crystals are dispensed and in that the quantity of dispensed liquid crystals is controlled based on the predicted value.
According to the invention, in a method for manufacturing a liquid crystal display utilizing the dispense-injection method, the support post height of columnar spacers can be measured, and an optimum quantity of liquid crystals can be dispensed based on the measured value. When spherical particles are dispersed, the dispersing density can be measured to dispense an optimum quantity of liquid crystals based on the same. Therefore, the present invention makes it possible to dispense an optimum quantity of liquid crystals on each liquid crystal display panel and to thereby eliminate the so-called foams attributable to a shortage of the quantity of liquid crystals and display irregularity attributable to an excessive quantity of liquid crystals, which allows stable mass production.